This invention relates generally to data transmission systems and more particularly to a communication system for transmitting information from a remote location on reflected radiant energy transmitted from another location.
Most known data transmission systems involve remote stations that are active; that is, the return signal with its attendant information is radiated from a remote station-mounted transmitter. Such systems are quite advantageous in some respects since the return signal is transmitted directly and is, thus, not subject to substantial attenuation nor to fluctuation inherent in the typical backscatter signal. However, active systems are not without disadvantages, primary among which are relative system complexity and cost, the likelihood of interference from other remote stations similarly situated, ease of detection, and the requirement of significant power.
Passive data transmission systems, i.e., systems which the return signal is merely a reflection of the signal transmitted, have overcome the problems of complexity, cost and detection, but have generally failed to solve the problem of specific remote station identification. Furthermore, these systems still require a source of power at the remote station in order to modulate the incident rf energy by rotating, oscillating, or vibrating the remote station's reflective surface.